Hi Graeme, > I have two 1-wire nets connected to raspberry PIs. The first includes > two DS1820 temperature sensors and a humidity sensor based on the > DS2438, which also incorporates an unspecified temperature sensor. > The second net just contains a humidity sensor with, again, > unspecified temperature sensor. > > At 13:56 yesterday, one DS1820 started registering the maximum 85°C, > and at 14:00 the second did the same (readings at 2-minute intervals). ... > I find it difficult to believe that two sensors should decide to give > up the ghost within 4 minutes of each other after several years of > operation, and the continued operation of other sensors seems to rule > out a voltage surge.
Looking at http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf, 85°C is the reset value of the temperature reading, e.g. after power on, before any conversion has been done. And a quick skim suggests conversions may take a while depending on the method of power supply, e.g. parasitic, or fail given inadequate power. How are the DS1820s being powered? See page 7/20. If parasitically, is Vdd grounded, or left floating? Are you properly waiting for the conversion to finish before reading? -- Cheers, Ralph. -- Next meeting: BEC, Bournemouth, Tuesday, 2020-01-07 20:00 Check to whom you are replying Meetings, mailing list, IRC, ... http://dorset.lug.org.uk/ New thread, don't hijack: mailto:dorset@mailman.lug.org.uk
